Computer graphics processing and selective visual display system – Computer graphics processing – Graph generating
Reexamination Certificate
1998-06-18
2001-07-31
Luu, Matthew (Department: 2679)
Computer graphics processing and selective visual display system
Computer graphics processing
Graph generating
C345S440000, C345S440000, C345S426000, C380S054000
Reexamination Certificate
active
06268866
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital watermarking system, and more particularly to a digital watermarking system for making a digital watermark in an image signal.
2. Description of the Related Art
As demands for protection of the copyright of contents of image signals have been on the rise in today's computer age, and yet as an exemplified technology for embedding descriptive information in signals of the media, development of the technology called “digital watermarking” has been carried forward. Generally, watermarking for image is regarded as a technology of modifying the image signal or data in such a form as to be impossible or extremely difficult to recognize by the human's peculiar visual sense.
The digital watermarking technology is exemplified by International Laid-Open Patent No. WO95-14289 disclosing a concept of combining a certain number of noise screens distributed at random in space regions and superimposing the composite a noise screen with an original image.
Further, in their copending U.S. patent application Ser. No. 08/534,894, the present applicant has proposed a digital watermarking technology of transforming an input image into frequency regions, then modifying part of the spectrum to make a digital watermark and then reversely transforming the frequency regions into the image (space regions).
In this last-named technology, the original image is transformed into frequency domain data using Fourier formation or DCT (discrete cosine transform), whereupon a significant value in the resulting spectrum is selected. The significant value means a value influential on the original image when the data is modified or deleted; this significant value is discriminated using, for example, the absolute value of the spectrum as a reference.
The selected absolute value of the spectrum is multiplied by (1+&agr;) where &agr; is a random number whose upper limit is approximately 0.1; the value of this random number and the position of the spectrum jointly define a digital watermark. Then the modified spectrum is transformed by reverse Fourier transform or reverse DCT to obtain a digital-watermarked image.
This method merely intends to weaken a digital watermark down to such a level not to be recognized by the human's visual sense, utilizing the lengthy depth of luminance level of the image.
According to the conventional technology, if the original image has few colors like, for example, a map image, it is impossible to make a digital watermark in such image data if not modified. Yet if a digital watermark could be made in the unmodified image data, the original image would have been greatly collapsed.
If the format of the image is transformed to secure an adequate luminance level, e.g., if the image of total eight colors represented by 3 bits of RGB (Red, Green, Blue) is transformed into an 24-bit image represented by 8 bits each of RGB with the hue kept unchanged, it is possible to secure such a depth of luminance level that a digital watermark can be made in the image. However, it would be possible to assume the primary colors of the original image; that is, the digital watermark can be deleted as by performing a simple quantification of color.
SUMMARY OF THE INVENTION
With the foregoing problems in view, an object of the present invention is to provide a digital watermarking system which is capable of effectively making a digital watermark in an original image of few colors.
According to a first aspect of the invention, the above object is accomplished by a digital watermarking system for making a digital watermark in an input image, comprising: a texture database previously containing a plurality of texture patterns in each of which the digital watermark is previously made; a color conversion table in which information for coordinating original colors of the input image with the texture patterns is previously registered; means for composing, based on contents of the textured base and of the color conversion table, a watermarked image in which the original colors of the input image are replaced with the corresponding texture patterns; and outputting means for retaining the watermarked image received from the composing means and outputting the watermarked image.
According to a second aspect of the invention, there is provided a digital watermarking system for making a digital watermark in an input image, comprising: a texture database previously containing a plurality of textured patterns; a color conversion table in which information for coordinating colors of the input image with the textured patterns is previously registered; watermarking means for making the digital watermark in each of the texture patterns received from the texture database; means for composing, based on contents of the color conversion table and an output of the watermarking means, a watermarked image in which the original colors of the input image are replaced with the corresponding watermarked texture patterns; and outputting means for retaining the watermarked image received from the composing means and for outputting the watermarked image.
According to a third aspect of the invention, there is provided a digital watermarking system for making a digital watermark in an input image, comprising: a texture database previously containing a plurality of texture patterns; a color conversion table in which information for coordinating original colors used in the input image with the texture patterns is registered; means for composing, based on contents of the texture database and of the color conversion table, a composite image in which the original colors of the input image are replaced with the corresponding texture patterns; watermarking means for making a digital watermark in the composite image to be outputted from the composing means; and outputting means for retaining the composite image in which the watermark is made by the watermarking means and for outputting such watermarked image.
According to a fourth aspect of the invention, there is provided a digital watermarking system for making a digital watermark in an input image, comprising: a texture database previously containing a plurality of texture patterns; a color conversion table in which information for coordinating original colors used in the input image with the texture patterns; a plurality of image buffers one for holding each of the texture patterns corresponding to a respective one of the original colors of the input image; watermarking means for making the digital watermark in each of the texture patterns held respectively by the image buffers; means for detecting the original colors of the input image one for each pixel of the input image; composing means for reading, from the image buffers corresponding to the original colors detected one for each pixel of the input image by the detecting means and holding the watermarked texture patterns, the corresponding pixels and for composing a composite image in which the original colors of the input image are replaced with the corresponding texture patterns; and outputting means for retaining the composite image outputted from the composing means and for outputting the composite image.
With the digital watermarking system of the invention, it is possible to make a digital watermark even in an input image of few colors at an adequately invisible level by increasing the depth of luminance level or of number of colors.
In the present invention, partly since the format of the image data is extended merely in depth of level and partly since the same color region of the original image is transformed into a region having a specified pattern of texture such that reproduction of the original image by performing color quantification again is difficult to achieve, it is possible to improve the resistance to requantization of color.
Preferably, the texture has many colors or varies in luminance level, so that a digital watermark can be made in an input image of few colors and the resistance to deleting the digital waterma
Chung Daniel J
Foley & Lardner
Luu Matthew
NEC Corporation
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